Power supply apparatus and method of controlling power supply circuit

ABSTRACT

The DC output of a power conversion unit is controlled based on a pulse signal generated by a PWM unit. An operations unit detects an output current Iout, and determines the operation mode of a load based on the detected current value. When the output current Iout is weak, a value smaller than usual is written to a cycle register. The PWM unit generates a pulse signal according to the data stored in the cycle register and an on-time register.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply apparatus provided witha power supply circuit for generating a DC output.

2. Description of the Related Art

A power supply apparatus such as an AC/DC converter, a DC/DC converter,a charger, etc. is popular in various fields. Generally, a power supplyapparatus should be small in loss. Particularly, it is very important toreduce loss in a power supply apparatus used in a portable personalcomputer, a terminal unit in a mobile communications device, etc.

FIG. 1 shows the configuration of the charger or the DC power supplyprovided in the conventional power supply apparatus. The charger and theDC power supply have the same basic configurations, and each includes anelectric power converter 510 and an analog circuit unit 520. In thisexample, the DC power supply is a DC/DC converter.

The electric power converter 510 includes a switching element (MOSFET)controlled according to the instruction from the PWM control circuit524; a rectifying diode; an inductor for storing/discharging energy; aresistor for detecting an inductor current or an output current; and anoutput capacitor for smoothing an output. While the switching element isin the ON state, the inductor current ramps up with the electric currentprovided for the load, thereby storing residual charge in the outputcapacitor. While the switching element is in the OFF state, the inductorcurrent ramps down and the electric charge stored in the outputcapacitor is discharged as necessary with the electric current providedfor the load.

The analog circuit unit 520 includes an amplifier 521 for amplifying aninductor current; an amplifier 522 for amplifying the difference betweenthe output from the amplifier 521 and a reference voltage Vref1; anamplifier 523 for amplifying the difference between the output voltageand a reference voltage Vref2; a PWM control circuit 524 for generatinga PWM signal for controlling the switching element based on the outputfrom these amplifiers, etc.; and an oscillator 525 for providing a clockat a predetermined frequency for the PWM control circuit 524.

When the output voltage drops below the reference voltage Vref2, the PWMcontrol circuit 524 makes the duty (duty cycle) of the PWM signal to beprovided for the switching element higher so that the inductor currentcan be increased and the output voltage will increase. On the otherhand, when the output voltage becomes higher than the reference voltageVref2, the PWM control circuit 524 makes the duty of the PWM signallower so that the inductor current can be reduced and the output voltagewill drop. Thus, the output voltage can be maintained at a constantlevel. When the PWM control circuit 524 detects an overcurrent based onthe output from the amplifier 522, it reduces the duty of the PWM signalor forcibly turns off the switching element.

Thus, an analog circuit has been used to control the output from acharger provided in the conventional power supply apparatus, or each DCpower supply.

As described above, an analog circuit has been used to control theoutput from the conventional power supply apparatus. Therefore, thecharacteristics or specification of a power supply circuit cannot beeasily changed. If they can be changed, a number of circuits have to beadded for amendments. Considering a smaller or a lower cost power supplyapparatus, the conventional technology has been impractical andunrealistic. Described below are some of the problems with theconventional power supply apparatus.

(1) Precision in Output Voltage

To control and maintain the output voltage of a power supply circuit,the output voltage is normally used as a feedback signal. However, atransfer function for a feedback system changes with external factors(input voltage, output current, temperature, etc.). Therefore, if suchfactors are not taken into account, oscillation may occur in thefeedback system.

Therefore, in the conventional power supply apparatus, an amplifier forthe feedback system is designed for the worst possible case in order toavoid the above described oscillation. However, this design reduces again in the normal operation, thereby lowering the precision in controlof an output voltage. This problem is due to the characteristic of anamplifier, which cannot be flexibly changed depending on various factorsuch as input voltage, output current, and temperature, in theconventional analog circuit.

(2) Error in Digitalizing Data

In newly developed technology, the functions of a conventional analogcircuit can be replaced with digital control. For example, a powersupply apparatus has been designed such that an output voltage as afeedback signal is converted into digital data from which numeral datafor control of a switching element is generated, and then, the switchingelement is controlled according to the numeral data. However, under thecontrol, an unavoidable digital error (quantization error) occurs. Theerror may cause a ripple in an output voltage.

To reduce the above described error, the quantization step should bereduced. However, reducing the quantization step raises the cost andincreases the electric power consumption in the power supply apparatus.

(3) Power Consumption

When an electric current required by a load is small, for example, inthe suspense mode of a personal computer, etc., it is particularlyimportant to reduce the power consumption of a power supply apparatusitself. This technology has long been studied, but has not beensatisfactorily developed, and therefore should be improved.

SUMMARY OF THE INVENTION

The present invention aims at providing a power supply apparatus forflexibly changing its characteristic or specification. It also aims atimproving the precision in output voltage. The present invention furtheraims at realizing smaller power consumption.

The power supply apparatus according to the present invention includes apower supply circuit for generating DC output according to a given pulsesignal; a conversion unit for converting a parameter relating to theoutput of the power supply circuit into digital data; an amplificationunit for amplifying the difference between the digital data obtainedfrom the conversion unit and a reference value; an adjustment unit foradjusting the characteristic of the amplification unit based on theinput voltage of the power supply circuit; and a generation unit forgenerating a pulse signal applied to the power supply circuit accordingto the amplification unit. The characteristic of the amplification unitcan be adjusted by an output current or the temperature around the powersupply apparatus in addition to the input voltage.

With the above described configuration, even if various parametersrelating to the operation of the power supply apparatus or the vicinalenvironment are changed, the precision in voltage control can beimproved because the gain and the phase of the power supply apparatuscan be optimized according to the changes.

The power supply apparatus, according to another aspect of the presentinvention, is based on the configuration including a power supplycircuit in which DC output is controlled by the PWM system. The powersupply apparatus includes a computation unit for computing the pulsewidth of a pulse signal to be provided for the power supply circuitbased on a parameter relating to output of the power supply circuit; acorrection unit for correcting the pulse width data computed by thecomputation unit according to a stored carry-over value; a conversionunit for converting the pulse width data corrected by the correctionunit into pulse width data that is a predetermined number of digits inlength; a generation unit for generating a pulse signal according to thepulse width data converted by the conversion unit, and providing it forthe power supply circuit; and a storage unit for storing the differencebetween the pulse width data corrected by the correction unit and thepulse width data converted by the conversion unit as a carry-over value.The conversion unit performs operations such as rounding up, roundingdown, rounding off, etc.

With the above described configuration, the carry-over value indicates adigital error (quantization error). The digital error is averaged by thecorrection unit. Therefore, the ripple of the output voltage can bereduced.

The power supply apparatus according to a further aspect of the presentinvention includes a power supply circuit for generating DC outputaccording to a given pulse signal; a detection unit for detecting theoperating state of the load connected to the power supply circuit; asampling unit for sampling a parameter for use in controlling the outputof the power supply circuit; a conversion unit for converting theparameter sampled by the sampling unit; an amplification unit foramplifying the difference between the digital data obtained from theconversion unit and the reference value; a characteristic adjustmentunit for adjusting the characteristic of the amplification unitaccording to the detection result from the detection unit; and ageneration unit for generating a pulse signal to be provided for thepower supply circuit based on the output from the amplification unit.

With the above described configuration, since the switching frequencychanges with the operating state of a load, the switching loss can bereduced, particularly if the output current is small.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of the charger or a DC power supplyprovided in the conventional power supply apparatus;

FIG. 2 shows the configuration of the power supply apparatus accordingto the present embodiment;

FIG. 3 shows the configuration of the electric power conversion unit;

FIG. 4 shows the control of the output voltage according to anembodiment of the present invention;

FIG. 5 shows the basic configuration of an operation unit;

FIG. 6A shows a practical circuit of an amplifier used in theconventional power supply apparatus;

FIG. 6B shows a digital filter equivalent to the amplifier generatedusing the IIR and shown in FIG. 6A;

FIG. 7 is a flowchart showing the basic operation performed by theoperation unit;

FIG. 8 shows the duty of a pulse signal;

FIG. 9A is a flowchart showing the operation performed by the pulsegeneration unit;

FIG. 9B shows an example of a generated pulse signal;

FIG. 10 shows the conventional power supply circuit;

FIG. 11 is a block diagram showing the transfer function of the powersupply apparatus shown in FIG. 10;

FIG. 12 shows an example of the G-Φ characteristic of an analogamplifier;

FIG. 13 shows an example of the table indicating the correspondencebetween an input voltage and the factor of a digital filter;

FIG. 14 is a flowchart of the process of controlling the output voltagewhile changing the characteristic of an amplifier based on the inputvoltage;

FIG. 15A shows the current dependency of the inductance of an amorphouscoil;

FIG. 15B shows an LC filter;

FIG. 15C shows the current dependency of the cut-off frequency;

FIG. 16 shows the frequency characteristic of the gain through the errordetection amplifier and the LC filter;

FIG. 17 is a flowchart of the process of controlling an output voltagewhile changing the characteristic of the amplifier depending on anoutput current;

FIG. 18A shows the configuration of the LC filter;

FIG. 18B shows the temperature dependency of the G-Φ characteristic ofthe LC filter;

FIG. 19 is a flowchart of the process of controlling an output voltagewhile changing the characteristic of the amplifier depending on thetemperature around the power supply apparatus;

FIG. 20 is a flowchart of the process of controlling an output voltagewhile changing the characteristic of the amplifier depending on theoutput voltage Vout of the power supply circuit;

FIG. 21 shows an example (of performing a rounding up operation) of theprocess of averaging a digital error;

FIG. 22 shows an example (of performing a rounding down operation) ofthe process of averaging a digital error;

FIG. 23 shows an example (of performing a rounding off operation) of theprocess of averaging a digital error;

FIG. 24 is a flowchart (of performing a rounding up operation) of theprocess of averaging a digital error;

FIG. 25 is a flowchart (of performing a rounding down operation) of theprocess of averaging a digital error;

FIG. 26 is a flowchart (of performing a rounding off operation) of theprocess of averaging a digital error;

FIG. 27 is a flowchart of the process of suppressing the digital errorwhile changing the pulse cycle;

FIG. 28 shows the function of collecting various parameters;

FIG. 29 shows a part of a program executed by the processor;

FIG. 30 shows the gain of the power supply apparatus obtained when aload is in the normal mode and the suspense mode;

FIG. 31 is a flowchart of the process of switching the operation of thepower supply apparatus depending on the operation mode of the load;

FIG. 32 shows the effect obtained by lowering the polling frequency;

FIG. 33 shows the sequence (1) of the process of switching the operationaccording to a notice from the load;

FIG. 34 shows the sequence (2) of the process of switching the operationaccording to a notice from the load;

FIG. 35 shows the LC filter using an amorphous core coil and a saturablecoil;

FIG. 36A shows the current dependency of the inductance;

FIG. 36B shows the current dependency of the cut-off frequency of the LCfilter;

FIG. 37 is a flowchart of the process of changing the switchingfrequency depending on an output current;

FIG. 38 is a flowchart of the process of computing the on-time of thepulse signal according to the updated switching frequency;

FIG. 39A shows the characteristic part of the synchronous power supplycircuit;

FIG. 39B shows the dead-off time;

FIG. 40 is a flowchart of the process of adjusting the dead-off time;

FIG. 41A shows the configuration of the PWM unit;

FIG. 41B shows the pulse signal generated by the PWM unit shown in FIG.41A; and

FIG. 42 is a flowchart of the operation of the PWM unit shown in FIG.41A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The power supply apparatus according to the present embodiment isprovided in a device such as a personal computer, etc., and comprises acharger for charging a battery provided in the device; and a pluralityof DC power supplies each generating a plurality of DC voltages used inthe device. The charger and DC power supplies can be generally referredto as a power supply circuit.

Each power supply circuit maintains each output voltage at a constantlevel by PWM (pulse width modulation). With PWM control of the outputvoltage, the duty (duty cycle) of the pulse provided for the powersupply circuit is normally modified based on the difference between theoutput voltage of the power supply circuit and the reference voltage.The power supply circuit adjusts the output voltage according to thepulse signal. That is, the feedback control is performed. According tothe present embodiment, the processor in the power supply apparatusperforms feedback control.

FIG. 2 shows the configuration of the power supply apparatus accordingto the present embodiment. A charger 10 charges a battery (not shown inFIG. 3) provided in the mainframe (personal computer, etc.) comprisingthe power supply apparatus. DC power supplies 20-1 through 20-n generaterespective DC voltages and each provides the generated DC voltage for aload. The charger 10 and the DC power supplies 20-1 through 20-n havethe same basic configurations, and comprise a PWM unit 11 and anelectric power conversion unit 12.

An I/O unit 31 receives an ON/OFF signal from a switch in the mainframecomprising the power supply apparatus, and notifies a processor (MPU) 41of the signal. An A/D conversion unit 32 converts the information (forexample, the remainder in the battery) relating to the battery chargedby the charger 10 into digital data, and transmits it to the processor41. A serial I/F unit 33 controls the transmission and reception of theinformation between the processor 41 and a higher-order appliance. Ahigher-order appliance refers to, for example, the CPU (main processor)in the mainframe comprising the power supply apparatus. In this example,the higher-order appliance transmits a signal indicating the reductionof an output voltage to the power supply apparatus when the operationmode is switched from the normal mode to the resume mode.

A multiplexing unit (MUX) 34 receives a parameter relating to the outputfrom the electric power conversion unit 12 in each power supply circuit(the charger 10 and the DC power supplies 20-1 through 20-n), an inputvoltage provided to each power supply circuit, and an output signal fromthe temperature sensor 46, and selects and outputs a designated signalaccording to the instruction from the processor 41. A parameter relatingto the output from the electric power conversion unit 12 is, forexample, an output voltage, an output current, etc. from each powersupply circuit. An A/D conversion unit 35 converts an output from themultiplexing unit 34 into digital data. The digital data converted bythe A/D conversion unit 35 is read by the processor 41. A segmentcontroller (SEG) 36 outputs a signal for display the amount of powerremaining in the battery, etc. on the display device not shown in FIG.2.

The processor 41 executes the program stored in ROM 42 using RAM 43. Inthe program executed by the processor 41, the procedure of the processfor controlling the operation of the power supply apparatus according tothe digital data from the I/O unit 31, the A/D conversion unit 32, theserial I/F unit 33, and the A/D conversion unit 35 is described. Theprogram is stored in the ROM area in FIG. 2, and can be designed to berewritten. Additionally, a DSP (digital signal processor) can be used asthe processor 41.

With the above described configuration, the processor 41 performs thesequence control for determining the powering order and disconnectingorder of a plurality of power supply circuits, the battery managementfor monitoring the amount of power remaining in a battery, the statemonitor/display of each power supply circuit, etc., and controls theoutput voltage of the power supply circuit so that the output voltagecan be maintained at a predetermined level. The power supply apparatusfurther comprises a clock generation unit 44 for generating a clocksignal, a timer 45, and a temperature sensor 46 for detecting thetemperature around the power supply apparatus.

FIG. 3 shows the configuration of the electric power conversion unit 12.The electric power conversion unit 12 is basically the same as theconventional electric power conversion unit shown in FIG. 1. That is,the electric power conversion unit 12 comprises a switching element 13(MOSFET in FIG. 3) controlled according to an instruction from the PWMunit 11, a rectifying diode D, an inductor L for storing/dischargingenergy, a resistor R for detecting an inductor current or an outputcurrent, and an output capacitor Cout for smoothing output. The electricpower conversion unit 12 comprises a driver (driving circuit) 14 fordriving the switching element 13 by amplifying a pulse signal from thePWM unit 11. The above described rectifying diode D can be replaced by aMOS transistor, etc. In this case, two MOS transistors are turned on/offaccording to switching control signals with opposite phases to eachother so that they cannot be simultaneously in an ON state.

A DC input is generated by an AC/DC converter or a DC/DC converter. Theoutput is provided for a load (including a battery).

With the above described configuration, the inductor current ramps upwhile the switching element 13 is in the ON state, and an electriccurrent is provided for a load with the residual charge stored in theoutput capacitor Cout. While the switching element 13 is in the OFFstate, the inductor current ramps down, and the electric current isprovided for the load with the charge stored in the output capacitorCout discharged as necessary. Therefore, the output voltage from theelectric power conversion unit 12, that is, the output voltage from eachpower supply circuit, can be modified according to the ON-to-OFF rate ofthe switching element 13.

The ON/OFF state of the switching element 13 can be controlled accordingto a pulse signal generated by the PWM unit 11. In the presentembodiment, H of the pulse signal corresponds to the ON state of theswitching element 13, and L of the pulse signal corresponds to the OFFstate of the switching element 13. Thus, the output voltage of the powersupply circuit can be controlled according to a ratio between a timeperiod during which the pulse signal is at H level and a time periodduring which the pulse signal is at L level.

In the existing PWM, the duty of a pulse signal provided for a switchingelement is normally used as a parameter for control of an output voltageof the power supply apparatus. The duty of a pulse signal is normallyrepresented as the ratio of the cycle of the pulse signal to the timeduring which the signal is at the H level. Therefore, according to thepresent embodiment, the duty of the pulse signal can be specified bydesignating the cycle of the pulse signal and the time during which thesignal is at the H level. According to the present embodiment, since theH level of the pulse signal corresponds to the ON state of the switchingelement, the time during which the pulse signal is at the H level can behereinafter referred to as an ON time. That is, according to the presentembodiment, the duty of the pulse signal is designated by specifying thecycle and the ON time of the pulse signal.

In the PWM, the cycle of a pulse signal is normally constant. In thiscase, the duty of the pulse signal can be adjusted by changing only theON time. However, in the power supply apparatus according to the presentembodiment, the switching frequency of the switching element 12 is notalways constant. Therefore, in this case, the duty of the pulse signalis determined by dynamically specifying the cycle and the ON time of thepulse signal. When the switching frequency is changed, the switchingfrequency is not unconditionally changed. This will be described laterin detail.

The electric power conversion unit 12 provides the controlled DC voltagefor a load not shown in the drawings, and outputs a parameter relatingto the output of the power supply circuit to the multiplexing unit 34.The output voltage is an electric potential of the output terminal ofthe power supply circuit. The output current is detected by, forexample, a current sensor. The current sensor can be realized by a shuntresistor. In this case, the value obtained by dividing the voltage atboth ends of the shunt resistor by the resistance value of the shuntresistor corresponds to the output current. These parameters (outputvoltage and output current) are converted by the A/D conversion unit 35into digital data. Then, the processor 41 reads the output from the A/Dconversion unit M35.

The output current can also be computed by transmitting each potentialat both ends of the resistor R shown in FIG. 3 to the processor 41through the A/D conversion unit 35, and computing through the processor41 the value by dividing by R the difference of the potential values atboth ends of the resistor R. The merit of this method is that there arefewer parts.

Explained simply, it is assumed that the electric power conversion unit12 outputs a voltage value corresponding to the output current Iout ofthe power supply circuit. The voltage value corresponding to the outputcurrent is converted into digital data by the A/D conversion unit 35 atthe instruction from the processor 41, and is read by the processor 41.

FIG. 4 shows the output voltage control according to the embodiment ofthe present invention. In this example, the charger 10 and an optionalone of the power supply circuits of the DC power supplies 20-1 through20-n of the charger 10 shown in FIG. 2 are explained. In FIG. 4, theelements not directly associated with the output voltage control areomitted.

The operation unit 50 is realized by the processor 41 executing apredetermined program stored in the ROM 42, and generates a signal(data) for control of the output voltage of the power supply circuit.Practically, the operation unit 50 calculates the duty of the pulsesignal for control of the switching element 13 of the electric powerconversion unit 12. A parameter used in the present embodiment is anoutput voltage and an output current of the power supply circuit.

The output voltage and current of the power supply circuit, the outputfrom the temperature sensor 46, and an applied voltage of a load areinput to the multiplexing unit 34. This operation is performed at asampling instruction from the processor 41. The sampling cycle is, forexample, 50 μs. The processor 41 transmits a selection signal (pollingsignal) to the multiplexing unit 34 to read required data from thesampled data. The multiplexing unit 34 selects an input signal accordingto the selection signal from the processor 41. In the input signalsinput to the multiplexing unit 34, the ‘output voltage’ is alwaysselected for each sampling, and other signals are selected as necessary.

The output from the multiplexing unit 34 is converted into digital databy the A/D conversion unit 35. The processor 41 reads the output fromthe A/D conversion unit 35.

When the processor 41 reads the digital data from the A/D conversionunit 35, it activates the operation unit 50, and calculates the duty ofthe pulse signal. The ‘output voltage’ is used in this operation.However, the ‘output current’, ‘temperature’, and ‘applied voltage to aload’ can also be used as necessary in an operation performed when theduty is determined. The method of performing the operation is describedlater.

When the operation unit 50 determines the duty of the pulse signal to beprovided for the switching element 13, it computes the ‘on-time’ basedon the duty. The on-time can be obtained by the following equation.

Ton=D/Ts

where D indicates the duty of the pulse signal provided for theswitching element 13, and Ts indicates the cycle of the pulse signal.

The ‘on-time Ton’ computed by the operation unit 50 is written to theon-time register 62 of the PWM unit 11.

The PWM unit 11 comprises a cycle register 61, the on-time register 62,a timer 63, and a pulse generation unit 64. The cycle register 61 is astorage area for storing cycle information which indicates the cycle ofan output pulse signal. The cycle of the pulse signal is the switchingcycle of the switching element 13, and is written to the cycle register61 in the initialization sequence of the power supply apparatus. Thecycle register 61 can be designed to be updated by the operation unit50. The on-time register 62 is a storage area for storing on-timeinformation which indicates the on-time computed by the operation unit50. The timer 63 counts the elapsed time from the leading edge to thetrailing edge of a generated pulse signal. The pulse generation unit 64uses the timer 63 to generate the pulse signal based on the cycleinformation stored in the cycle register 61 and the on-time informationstored in the on-time register 62.

As described above, the output from the PWM unit 11 is used as aswitching signal for control of the switching element 13 in the electricpower conversion unit 12.

FIG. 5 shows the basic configuration of the operation unit 50. Theoperation unit 50 comprises a reference voltage register 51, a digitalfilter 52, and a pulse width computation unit 53. The reference voltageregister 51 stores a reference value Vref indicating an output voltageto be maintained by the power supply circuit. Assuming that, forexample, the output voltage to be maintained by the power supply circuitis 5V, the reference value Vref refers to the digital data which will beobtained if ‘5V’ is input to the A/D conversion unit 35.

The output voltage of the power supply circuit is feedback controlledsuch that the voltage can match the reference value Vref. That is, theoperation unit 50 obtains and outputs the duty (on-time of the pulsesignal provided for the switching element 13) depending on which theoutput voltage Vout of the power supply circuit matches the referencevalue Vref. Therefore, when the reference value Vref is changed, theoutput voltage Vout of the power supply circuit is changedcorrespondingly.

The digital filter 52 amplifies and outputs the difference between theoutput voltage Vout and the reference value Vref. The digital filter 52is basically designed to implement the characteristic (especially theG-Φ characteristic) of the amplifier 523 used in the conventional powersupply apparatus shown in FIG. 1. The pulse width computation unit 53computes the ‘on-time Ton’ based on the output from the digital filter52. The on-time refers to a time during which the switching element 13is in an ON state on the switching cycle of the switching element 13.The pulse width computation unit 53 writes the on-time to the on-timeregister 62 of the PWM unit 11.

Described below is the method of realizing the operation unit 50. Asdescribed above, the digital filter 52 is basically designed toimplement the characteristics as is (especially the G-Φ characteristic)of the amplifier 523 used in the conventional power supply apparatusshown in FIG. 1. FIG. 6A shows an example of a practical circuit of theamplifier 523 used in the conventional power supply apparatus. Thetransfer function of the analog amplifier is described below.$\begin{matrix}{G_{(s)} = {\frac{R_{1} + R_{2}}{R_{1}} \cdot \frac{1 + {s\quad c\quad \left( {{R_{3} + R_{1}}//R_{2}} \right)}}{1 + {s\quad c\quad \left( {R_{2} + R_{3}} \right)}}}} \\{= \frac{\alpha \quad \left( {1 + {s\quad \gamma}} \right)}{1 + {s\quad \beta}}}\end{matrix}$${G\left( {j\quad \omega} \right)} = \frac{\alpha \quad \left\{ {1 + {\omega^{2}\beta \quad \gamma} + {j\quad \omega \quad \left( {\gamma - \beta} \right)}} \right\}}{1 + {\omega^{2}\beta^{2}}}$$\left( {{\alpha = \frac{R_{1} + R_{2}}{R_{1}}},{\gamma = {c\quad \left( {{R_{3} + R_{1}}//R_{2}} \right)}},{\beta = {c\quad \left( {R_{2} + R_{3}} \right)}}} \right)$

As a digital filter, for example, an FIR (finite impulse response)filter and an IIR (infinite impulse response) filter are popular. Thedigital filter 52 can be realized by using either of them, the IIRfilter is used in the present embodiment.

To assign the characteristics of an analog amplifier (analog filter) toan IIR filter, the s-z transformation is adopted. The s-z transformationrefers to a method of converting a transfer function G(s) of an analogfilter in an s area into a z area.

FIG. 6B shows a digital filter which is generated using the IIR and isequivalent to the amplifier (analog filter) shown in FIG. 6A. Thedigital filter comprises an adder 71, factor multipliers 72 through 74,and unit delay elements 75 and 76. The method of replacing the amplifiershown in FIG. 6A with the digital filter shown in FIG. 6B is well-known,but is described below for confirmation.

Described below is the transfer function in the area.${\text{~~~~}s} = \frac{2\left( {1 - Z^{- 1}} \right)}{T_{s}\quad \left( {1 + Z^{- 1}} \right)}$$\begin{matrix}{\quad {G_{(Z)} = {\frac{R_{1} + R_{2}}{R_{1}} \cdot \frac{T_{s} + {2c\quad \left( {{R_{3} + R_{1}}//R_{2}} \right)} + {\left\{ {T_{s} - {2c\quad \left( {{R_{3} + R_{1}}//R_{2}} \right)}} \right\} \cdot Z}}{T_{s} + {2c\quad \left( {R_{2} + R_{3}} \right)} + {\left\{ {T_{s} - {2c\quad \left( {R_{2} + R_{3}} \right)}} \right\} \cdot Z^{- 1}}}}}} \\{= \frac{\alpha \cdot \left\{ {T_{s} + {2\gamma} + {\left( {T_{s} - {2\gamma}} \right) \cdot Z^{- 1}}} \right\}}{T_{s} + {2\beta} + {\left( {T_{s} - {2\beta}} \right) \cdot Z^{- 1}}}} \\{= {\alpha \cdot \frac{T_{s} - {2\gamma}}{T_{s} - {2\beta}} \cdot \frac{\frac{T_{s} + {2\gamma}}{T_{s} - {2\gamma}} + Z^{- 1}}{\frac{T_{s} + {2\beta}}{T_{s} - {2\beta}} + Z^{- 1}}}} \\{= {\alpha \cdot a \cdot \frac{b + Z^{- 1}}{c + Z^{- 1}}}}\end{matrix}$$\text{~~~~}\left( {{a = \frac{T_{s} - {2\gamma}}{T_{s} - {2\beta}}},{b = \frac{T_{s} + {2\gamma}}{T_{s} - {2\gamma}}},{c = \frac{T_{s} + {2\beta}}{T_{s} - {2\beta}}}} \right)$$\begin{matrix}{\quad {{G\left( ^{j\quad \omega \quad T_{s}} \right)} = {\alpha \cdot a \cdot \frac{b + {\cos \quad \left( {\omega \quad T_{s}} \right)} - {{j \cdot \sin}\quad \left( {\omega \quad T_{s}} \right)}}{c + {\cos \quad \left( {\omega \quad T_{s}} \right)} - {{j \cdot \sin}\quad \left( {\omega \quad T_{s}} \right)}}}}} \\{= \frac{{\alpha \cdot a}\quad \left\{ {{\left( {b + {\cos \quad \left( {\omega \quad T_{s}} \right)}} \right) \cdot \left( {c + {\cos \quad \left( {\omega \quad T_{s}} \right)}} \right)} + {\sin^{2}\left( {\omega \quad T_{s}} \right)} + {j\quad {\left( {b - c} \right) \cdot}}} \right.}{\left( {c + {\cos \quad \left( {\omega \quad T_{s}} \right)}} \right)^{2} + {\sin^{2}\left( {\omega \quad T_{s}} \right)}}}\end{matrix}$

The following results are obtained from the above listed equations (1)and (2). $\begin{matrix}\begin{matrix}{Y_{(n)} = {{\frac{\alpha \cdot a \cdot b}{c} \cdot X_{(n)}} + {\frac{\alpha \cdot a}{c} \cdot X_{({n - 1})}} - {\frac{1}{c} \cdot Y_{({n - 1})}}}} \\{= {{A \cdot X_{(n)}} + {{B \cdot X_{({n - 1})}}\quad {C \cdot Y_{({n - 1})}}}}}\end{matrix} & (3) \\{A = {\frac{R_{1} + R_{2}}{R_{1}} \cdot \frac{T_{s} + {2c\quad \left( {{R_{3} + R_{1}}//R_{2}} \right)}}{T_{s} + {2c\quad \left( {R_{2} + R_{3}} \right)}}}} & (4) \\{B = {\frac{R_{1} + R_{2}}{R_{1}} \cdot \frac{T_{s} - {2c\quad \left( {{R_{3} + R_{1}}//R_{2}} \right)}}{T_{s} + {2c\quad \left( {R_{2} + R_{3}} \right)}}}} & (5) \\{C = {- \frac{T_{s} - {2c\quad \left( {R_{2} + R_{3}} \right)}}{T_{s} + {2c\quad \left( {R_{2} + R_{3}} \right)}}}} & (6)\end{matrix}$

The configuration shown in FIG. 6B can be obtained from equation (3)above. The factors set by the factor multipliers 72 through 74 arerepresented by equations (4) through (6) above.

Equation (3) above (including equations (4) through (6)) is described ina software program, and the digital filter 52 can be realized by theprocessor 41 performing the program. Thus, according to the presentembodiment, the operations and the characteristics of an analogamplifier used in the conventional power supply apparatus are describedby a software program, and the program is executed to provide theoperations of the analog amplifier. Therefore, the characteristics ofthe analog amplifier can be changed simply by rewriting the program.

FIG. 7 is a flowchart showing the operation of the operation unit 50. Inthis example, as described by referring to FIG. 4, an optional powersupply circuit in the DC power supplies 20-1 through 20-n is selectedfor description. It is assumed that the reference value Vref is storedin the reference voltage register 51. The process shown in thisflowchart is performed for each of the very short intervals (forexample, 50 μs.) by a timer interruption, etc.

An output voltage Vout is obtained in step S1. Practically, theprocessor 41 first notifies the multiplexing unit 34 that the outputvoltage Vout of the power supply circuit is selected. The output voltageVout from the power supply circuit, the output current Iout from thepower supply circuit, the input voltage Vin provided for the powersupply circuit, and the output signal from the temperature sensor 46 areinput to the multiplexing unit 34. According to the notification fromthe processor 41, the multiplexing unit 34 outputs the output voltagefrom the power supply circuit to the A/D conversion unit 35. Theprocessor 41 reads digital data (output voltage Vout), that is, theconversion result from the A/D conversion unit 35.

The reference value Vref is obtained from the reference voltage register51 in step S2. In step S3, the difference between the output voltageVout obtained in step S1 and the reference value Vref obtained in stepS2 is computed. In step S4, a digital filter operation is performed. Inthis process, the computation result in step S3 is input to the digitalfilter shown in FIG. 6B. The computation result in step S3 issubstituted for the equation (3) above.

In step S5, the duty of the pulse signal generated by the PWM unit 11 iscomputed based on the result of the operation by the digital filter.Briefly described below by referring to FIG. 8 is the duty of the pulsesignal.

The pulse signal is normally generated using a triangular wave in ananalog circuit. Using a triangular wave, the process performed in stepS5 corresponds to the process of comparing the level of the triangularwave with the result of the operation by the digital filter. Assumingthat the output from the digital filter 52 is Vamp, the cycle of thetriangular wave is T, and the maximum value of the triangular wave isVmax, the duty of the generated pulse signal is represented by thefollowing equation.

D=Ton/T=(Vmax−Vamp)/Vmax  (7)

Therefore, according to the present embodiment, the duty of a pulsesignal is obtained using a predetermined maximum value Vmax of thetriangular wave by substituting the output from the digital filter 52 inthe equation (7) above.

In step S6, it is checked whether or not the duty obtained in step S5 isequal to or smaller than a predetermined maximum set value. If it isdetermined that the duty obtained in step S5 is equal to or smaller thanthe predetermined maximum set value, then the on-time Ton is computedusing the computed duty from equation (7) above in step S7. That is, theoperation Ton=D·T is performed. However, if the duty obtained in step S5is larger than the predetermined value, the on-time Ton is obtainedusing the maximum set value Dmax instead of the duty D obtained in stepS5. That is, the operation Ton=Dmax·T is performed.

In step S9, the on-time computed in step S7 or S8 is written to theon-time register 62 in the PWM unit 11.

The processes in the above described steps S1 through S9 are repeated atvery short predetermined intervals. Therefore, the on-time correspondingin real time to the output voltage of a power supply circuit isconstantly written to the on-time register 62. The above describedprocess is cyclically performed on a plurality of power supply circuits.Each operation result is written to the on-time register 62 of the PWMunit 11.

FIG. 9A is a flowchart showing the operations of the pulse generationunit 64. In step S11, the timer 63 is activated. Upon activation of thetimer, the output from the PWM unit 11 is switched from the L level tothe H level in step S12. In steps S13 and S14, the output from the PWMunit 11 is maintained at the H level until the time that has elapsedsince the activation of the timer 63 reaches the on-time Ton stored inthe on-time register 62.

When the time that has elapsed since the activation of the timer 63reaches the on-time Ton, the output from the PWM unit 11 is switchedfrom the H level to the L level in step S15. In steps S16 and S17, theoutput from the PWM unit 11 is maintained at the L level until the timethat has elapsed since the activation of the timer 63 reaches the cycleT stored in the cycle register 61. When the time that has elapsed sincethe activation of the timer reaches the cycle T, control is passed tostep S11 to re-activate the timer 63.

The pulse signal shown in FIG. 9B is generated by repeatedly performingthe above described processes. According to the pulse signal, theswitching element 13 of the electric power conversion unit 12 iscontrolled.

As described above, the power supply apparatus according to the presentembodiment generates a pulse signal to control the switching element 13in a software process. Therefore, the output voltage of each powersupply circuit, and the switching frequency, the responsecharacteristics of the switching element 13 can be easily changed onlyby re-writing the program to be executed by the processor 41. Forexample, an output voltage can be determined by setting the referencevalue Vref. A switching frequency can be determined by setting thefrequency of the triangular wave shown in FIG. 8. A responsecharacteristic changes with a factor of the digital filter shown in FIG.6B.

Thus, the operation unit 50 and the PWM unit 11 of the power supplyapparatus according to the present embodiment performs the functions ofthe analog unit of the conventional power supply apparatus. As a result,the entire circuit can be smaller. Furthermore, according to the presentembodiment, the analog unit of the conventional power supply apparatusis described in the software program. Therefore, even if it is necessaryto change the function provided by the conventional analog circuit, itcan be easily changed only by re-writing the program.

Described below are the operations directly related to the power supplyapparatus according to the present invention. The power supply apparatusaccording to the present invention is based on the configurationexplained by referring to FIGS. 2 through 9. The characteristics andspecification of the power supply apparatus can be flexibly changed bythe operations of the operation unit 50, that is, by the program to beexecuted by the processor 41. Three embodiments are described below.

First Embodiment

The first embodiment relates to the technology of optimizing therelationship between the gain and the phase of a power supply apparatusindependent of external factors (input voltage, output current,temperature, output voltage, etc.), and more specifically to thetechnology of improving the output voltage precision by obtaining thelargest possible gain without the oscillation of a feedback system forcontrolling the output of a power supply circuit.

FIG. 10 shows the circuit of the conventional power supply apparatus.This figure shows furthermore in detail the feedback system forcontrolling an output voltage shown in FIG. 1. In FIG. 10, the portionsnot directly related to the feedback system are omitted.

A resistor network (voltage divider) 81 divides the voltage Vout of theoutput terminal of the power supply circuit. Practically, the resistornetwork 81 outputs the voltage expressed by the following equation whenthe switch SW is in an opening state.

V=Vout·R 6/(R 5+R 6)

The resistor network 81 outputs the voltage expressed by the followingequation when the switch SW is in a closing state.

V=Vout·Rx/(R 5+Rx)

Rx=R 6·R 7/(R 6+R 7)

The opening and closing states of the switch SW can be controlled by,for example, an instruction from the user or the personal computerincluding the power supply apparatus. Based on the state of the switchSW, the value of the output voltage to be maintained can be varied.

The amplifier 523 has been described by referring to FIG. 6A. Thecharacteristics of its gain and phase (G-Φ characteristic) depend onresistors R1 through R4 and a capacitance C1. Although a resistor R4 isnot shown in FIG. 6A, it is obvious that one of ordinary skill in theart can provide the resistor when a reference voltage is input. Aresistor Rc is a serial resistor (ESR) to the output capacitor Cout. InFIG. 10, a MOS transistor replaces the rectifying diode shown FIG. 1.However, the replacement is not significant in the present invention.

FIG. 11 is a block diagram showing the transfer function of the powersupply apparatus shown in FIG. 10. In FIG. 11, Fr, Fi, Fd, and Fp aretransfer functions in the electric power conversion unit 12. Among them,Fp is a factor that depends on the input voltage Vin. Fp is also atransfer function of an LC filter comprising an inductor L and an outputcapacitor Cout. These transfer functions are represented as follows.$F_{r} = {\frac{Vout}{R^{2}} \cdot \left( {{s\quad L} + r} \right)}$F_(i) = D F_(d) = Vin$F_{p} = \frac{k_{p} \cdot \left( {s + \frac{1}{C \cdot R_{c}}} \right)}{s^{2} + {a_{1} \cdot s} + a_{2}}$$k_{p} = \frac{R \cdot R_{c}}{L\quad \left( {R + R_{c}} \right)}$$a_{1} = {\frac{r}{L} + \frac{R \cdot R_{c}}{L\quad \left( {R + R_{c}} \right)} + \frac{1}{C\left( {R + R_{c}} \right)}}$$a_{2} = \frac{r + R}{L\quad C\quad \left( {R + R_{c}} \right)}$

F1 is a transfer function of a resistor network. Fe is a transferfunction of the amplifier 523. Fm is a transfer function of the PWMcontrol circuit 524. These transfer functions are represented asfollows.

The open loop transfer function Ga(s) of the feedback system of thepower supply circuit is represented as follows.

Ga(s)=F 1·Fe·Fm·FdΦFp

With the above described configuration, the gain and phase of thetransfer function Ga(s) change with the input voltage Vin, the outputcurrent Iout, the temperature around the power supply apparatus, and the${F_{1}\left( {{SW}\text{:}{OPEN}} \right)} = \frac{R_{6}}{R_{5} + R_{6}}$${{F_{1}\left( {{SW}\text{:}{CLOSE}} \right)} = \frac{R_{x}}{R_{5} + R_{x}}};{R_{x} = \frac{R_{6} - R_{7}}{R_{6} + R_{7}}}$$F_{e} = {K_{e} \cdot \frac{S + \frac{R_{3} + R_{4}}{c_{1}\left( {{R_{3} \cdot R_{2}} + {R_{2} \cdot R_{A}} + {R_{A} \cdot R_{3}}} \right)}}{S + \frac{1}{C_{1}\left( {R_{3} + R_{2}} \right)}}}$$K_{e} = \frac{{R_{3} \cdot R_{2}} + {R_{2} \cdot R_{A}} + {R_{A} \cdot R_{3}}}{R_{A} \cdot \left( {R_{3} + R_{2}} \right)}$R_(A) = R₄//R₁

voltage Vout to be maintained by the power supply apparatus. Actually,the transfer function Fd changes with an input voltage. The transferfunction Fp changes with the output current lout and the temperaturearound the power supply apparatus. The transfer function F1 changes withthe voltage Vout to be maintained.

With the above described configuration of the power supply apparatus, anoscillation should be suppressed in the above described feedback system.The oscillation in the feedback system arises when the phase of thetransfer function Ga(s) satisfies a predetermined condition. Thecondition of an oscillation is, as it is well known, the phase delay=0(2π) for positive phase amplification, and the phase delay=π for a phaseshift. Since the power supply apparatus according to the presentembodiment belongs to the positive phase amplification, an oscillationarises when the phase delay reaches 2π in the transfer function Ga(s).

Each transfer function forming part of the transfer function Ga(s) hasits own gain and phase depending on each frequency. For example, the G-Φcharacteristic of the amplifier 523 is shown in FIG. 12.

To increase the reliability of the power supply apparatus, it isnecessary under all conditions to completely suppress the oscillation inthe feedback system. To attain this, the amplifier 523 is normallydesigned to have a characteristic to suppress the oscillation in thefeedback system on the assumption that each of the transfer functionsforming part of the transfer function Ga(s) is assigned the worstpossible condition. Practically, the gain of the amplifier 523 isdetermined based on the worst possible condition for each transferfunction. Therefore, under normal conditions, the gain of the amplifier523 is set to a low value.

The first embodiment of the present invention has been developed tosolve the above described problem, and designed to change thecharacteristic of the amplifier depending on the condition assigned toeach transfer function forming part of the transfer function Ga(s).According to the present embodiment, the function of the above describedamplifier is implemented in the digital filter shown in FIG. 5, and thecharacteristic of the amplifier is adjusted by changing the factor (suchas, factors A, B, C in equation (3)) of the digital filter.

When the input voltage Vin applied to the power supply circuit changes,the phase delay of the transfer function Ga(s) changes with the transferfunction Fd. Normally, in the power supply apparatus, when the inputvoltage Vin becomes high, the gain G becomes larger. As a result, aprolonged phase delay satisfies the condition for generating anoscillation in the feedback system. In this case, the input voltage Vinof the power supply circuit is monitored, and the characteristic of thedigital filter 52 is optimized depending on the voltage according to thepresent embodiment. Practically, appropriate factors are selected as thefactors A through C in the equation (3) above. The equation (3) above isdescribed in the program executed by the processor 41, and relates tothe characteristic of the digital filter 52.

The relationship between the input voltage Vin and the above describedfactors A through C is preliminarily obtained through simulation, etc.and the result is stored in a table as shown in FIG. 13. The table is,for example, stored in the ROM 42. The operation unit 50 periodicallydetects the input voltage Vin, retrieves factors A through C from thetable shown in FIG. 13 using the detected voltage as a key, and updatesthe above described equation (3).

FIG. 14 is a flowchart of the process of controlling the output voltagewhile changing the characteristic of the amplifier depending on theinput voltage. This process is performed at predetermined intervals by atimer interruption, etc.

In step S21, the voltage Vout is obtained. This process is the same asthe process in step S1 shown in FIG. 7. In step S22, the input voltageVin is obtained. This process corresponds to a process of transmitting apolling signal to the multiplexing unit 34, and then reading the digitaldata corresponding to the input voltage from the A/D conversion unit 35.

In step S23, the table shown in FIG. 13 is accessed using the inputvoltage data obtained in step S22 as a key to extract the factors Athrough C. In step S24, an equation describing a digital filter usingeach factor extracted in step S23 is updated. Then, in step S25, adigital filter operation is performed for the obtained input voltageVin. In steps 26 and 27, which are the same as steps S5 through S9 shownin FIG. 7, the on-time of a pulse signal is computed and written to theon-time register 62 of the PWM unit 11.

In the above described process, the characteristic of the digital filter52 is always optimized in response to a change in the input voltage.Therefore, an oscillation of the feedback system can be suppressed whilea large gain is maintained. In the above described flowchart, since theinput voltage is not suddenly changed, it is not necessary to performthe process of changing the characteristic of a digital filter dependingon the input voltage Vin, that is, the process in steps S22 through S24,each time the on-time is computed.

In a power supply apparatus, an inductor L that has an inductance thatchanges with an electric current can be used. For example, an amorphouscore coil has a characteristic in which its inductance is reduced if theelectric current becomes strong.

If the inductor L with the above described characteristic is used, thetransfer function Fp changes with the output current Iout provided fromthe power supply circuit to a load, thereby changing the phase delay ofthe transfer function Ga(s).

FIG. 15A shows the current dependency of the inductance of an amorphouscore coil. Using an inductor having such a characteristic, the cut-offfrequency of the LC filter shown in FIG. 15B is shown in FIG. 15C. Thatis, the cut-off frequency of the LC filter is low when the outputcurrent Iout is weak, and is high when the output current Iout becomesstrong. Therefore, in the power supply apparatus shown in FIG. 11, whenthe output current Iout is weak, the cut-off frequency of the LC filterbecomes low. As a result, the phase delay is developed and the conditionfor generating an oscillation in the feedback system is also developed.

FIG. 16 shows the frequency characteristic of a gain by an errordetecting amplifier (amplifier 523) and an LC filter. As describedabove, the cut-off frequency of the LC filter depends on an outputcurrent. In FIG. 16, the cut-off frequencies when the output current isweak, medium, and strong are represented by fcs, fcm, and fcLrespectively.

When the output current Iout is weak, the feedback system tends tosatisfy the condition of generating an oscillation due to the phasedelay, as described above. Therefore, with the conventional analogconfiguration in which the G-Φ characteristic cannot be dynamicallychanged, the characteristic of the amplifier is determined based on aweaker output current Iout. That is, in FIG. 16, the resistance and thecapacitance as shown in FIG. 6A are determined such that the cut-offfrequency can be fcas, and an amplifier having the gain characteristicindicated by broken lines is used. As a result, when the output currentIout becomes strong, a necessary gain may not be obtained, and theprecision of the control of the output voltage Vout may not besatisfactory.

According to the present embodiment, the output current Iout of thepower supply apparatus is monitored, and the characteristic of thedigital filter 52 is optimized depending on the electric current.Practically, the factors A through C in the equation (3) above areappropriately selected such that the gain is larger when the outputcurrent becomes strong. That is, it is set so that the gain of the errordetecting amplifier has the characteristic indicated by the wave lines,solid lines, and dash-and-point lines when the output current Iout ofthe power supply circuit is weak, medium, and strong respectively. Thesettings depend on the cut-off frequency (fcas, fcam, fcaL) of the errordetecting amplifier. The cut-off frequency of the amplifier is shown inFIG. 12.

The relationship between the output current Iout and the above describedfactors A through C is preliminarily obtained by simulation, etc. in themethod described above by referring to FIG. 16, and stored in the table.The configuration of the table is basically the same as theconfiguration shown in FIG. 13, but is different in that the factors Athrough C are stored using the output current as a key. The operationunit 50 periodically detects the output current Iout, retrieves thefactors A through C using the current as a key, and updates the equation(3) above.

FIG. 17 is a flowchart of the process of controlling the output voltagewhile changing the characteristic of the amplifier depending on theoutput current. This process is performed by replacing steps S22 throughS24 shown in FIG. 14 with steps S31 through S33. In step S31, the outputcurrent Iout is obtained. This process corresponds to the process oftransmitting a polling signal to the multiplexing unit 34, and thenreading digital data corresponding to the output current from the A/Dconversion unit 35. In step S32, factors A through C are extracted usingthe output current data obtained in step S31 as a key. In step S33, theequation relating to the digital filter is updated using each factorextracted in step S32.

In the equation described above, the characteristic of the digitalfilter 52 is always optimized for the change in the output current.Therefore, the oscillation of a feedback system with a large gain can besuppressed.

Normally, the capacitor has resistance elements (resistor Rc in FIG. 10)to be serially connected to the capacitance elements. The serialresistor can be referred to as an ESR. The resistance value of the ESRdepends on the temperature. For example, the resistance value of the ESRof a field capacitor becomes larger when the temperature drops, andbecomes smaller when the temperature rises.

The resistance value of the ESR of the output capacitor Cout used in theabove described LC filter also changes with the temperature. Therefore,when the temperature around the power supply apparatus changes, thetransfer function Fp also changes, thereby changing the phase delay ofthe transfer function Ga(s).

FIG. 18B shows the temperature dependency of the G-Φ characteristic ofthe LC filter shown in FIG. 18A. The phase delay caused by the LC filteris small when the resistance value of the ESR is large, and becomeslarger when the resistance value of the ESR is smaller. That is, thephase delay caused by the LC filter is small when the temperature islow, and large when the temperature is high if a field capacitor is usedas an output capacitor Cout. Therefore, in the power supply apparatusshown in FIG. 11, the phase delay becomes large when the temperature inthe vicinity of the power supply apparatus rises, thereby reaching theconditions which generate an oscillation in the feedback system.

According to the present embodiment, the temperature around the powersupply circuit is monitored, and the characteristic of the digitalfilter 52 is optimized depending on the temperature. Practically, thefactors A through C in the equation (3) above are appropriately selectedsuch that the gain becomes larger when the temperature around the powersupply circuit drops. To change the gain of the digital filter 52, themethod used to change the cut-off frequency is the same as the methodused when the gain is changed according to the output current.

The relationship between the temperature around the power supplyapparatus and the above described factors A through C is preliminarilyobtained by simulation, etc., and stored in the table. The table isbasically the same as the configuration shown in FIG. 13, but thefactors A through C are stored using the temperature around the powersupply apparatus as a key. The operation unit 50 periodically detectsthe temperature around the power supply apparatus, retrieves the factorsA through C using the detected temperature as a key, and updates theequation (3) above.

FIG. 19 is a flowchart of the process used to control the output voltagewhile changing the characteristic of the amplifier depending on thetemperature around the power supply apparatus. This process is performedby replacing steps S22 through S24 shown in FIG. 14 with steps S41through S43. In step S41, the temperature around the power supplyapparatus is obtained. This process corresponds to the process oftransmitting a polling signal to the multiplexing unit 34, and thenreading digital data corresponding to the output current from the A/Dconversion unit 35. The temperature around the power supply apparatus isdetected by the temperature sensor 46. In step S42, factors A through Care extracted using the temperature data obtained in step S41 as a key.In step S43, the equation relating to the digital filter is updatedusing each factor extracted in step S42.

In the equation described above, the characteristic of the digitalfilter 52 is always optimized for the change in temperature around thepower supply apparatus. Therefore, an oscillation of the feedback systemwith a large gain can be suppressed.

A power supply apparatus may be able to change the output voltage to bemaintained by the user operation or by an instruction from the CPU ofthe personal computer including the power supply apparatus. In the powersupply apparatus shown in FIG. 10, the settings of the output voltage tobe maintained can be switched by the opening or the closing state of theswitch SW in the resistor network 81.

When the output voltage to be maintained changes, the gain of thetransfer function Ga(s) is reduced by changing the gain of the transferfunction F1 as described above. Practically, when the output voltage tobe maintained increased, the gain is reduced because the partialpressure ratio of the resistor network 81 drops. Therefore, if theoutput voltage is overestimated, the precision in output voltage Vout islowered.

According to the present embodiment, the output voltage is monitored,and the characteristic of the digital filter 52 is optimized accordingto the voltage. Practically, the factors A through C in the equation (3)above are appropriately selected such that the gain becomes larger whenthe voltage to be maintained becomes higher.

The relationship between the output voltage of the power supply circuitand the above described factors A through C is preliminarily obtained bysimulation, etc., and stored in the table. The configuration of thetable is basically the same as the configuration shown in FIG. 13, butthe factors A through C are stored using the output voltage as a key.The operation unit 50 periodically detects the output voltage of thepower supply apparatus, extracts the factors A through C using thevoltage as a key, and updates the equation (3) above.

FIG. 20 is a flowchart of the process of controlling the output voltagewhile changing the characteristic of the amplifier depending on theoutput voltage Vout of the power supply circuit. This process isperformed by replacing steps S22 through S24 shown in FIG. 14 with stepsS51 through S52. In step S51, factors A through C are extracted usingthe output voltage data obtained in step S21 as a key. In step S52, theequation relating to the digital filter is updated using each factorextracted in step S51.

In the above described process, the characteristic of the digital filter52 is always optimized even if the setting of the output voltage to bemaintained by the power supply circuit is changed. Therefore, a largegain can be constantly obtained, and the output voltage can becontrolled in high precision.

In the above described embodiment, the characteristic of the digitalfilter can be changed for any one of the input voltage, output current,environmental temperature, and output voltage as a parameter. However,it is intended that the power supply apparatus according to the presentinvention be designed to function appropriately even when a plurality offactors change simultaneously.

Second Embodiment

The second embodiment relates to the technology of reducing a digitalerror and a ripple in the power supply apparatus for digital-controllingthe output from the power supply circuit.

The configuration of the power supply apparatus according to the presentembodiment is shown in FIG. 4, and digitally computes the on-time (pulsewidth) of the pulse signal to be provided for the switching element 13using the output voltage as a feedback signal. Then, a pulse signal witha computed on-time is generated and provided for the switching element13, thereby maintaining the output voltage of the power supply circuitat a constant value.

However, when an analog parameter such as an output voltage is replacedwith digital data, a digital error (quantization error) necessarilyoccurs. The error can be predicted by the resolution (quantization step)of a digital process. For example, when the resolution of a digitalprocess is 100 ns in a power supply apparatus, and when the computationresult of the on-time by the operation unit 50 is 3.34 μs, the PWM unit11 generates a pulse signal with a pulse width of 3.3 μs or 3.4 μs. Suchan error causes a ripple of the output of the power supply apparatus. Inthe above described example, assuming that the input voltage is 18 voltsat maximum and the cycle of the pulse signal is 20 μs, the maximum valueof the ripple due to the digital error is represented as follows.$\begin{matrix}{{Vripple} = {18\quad V \times \left( {100\quad {{ns}/20}\quad {µs}} \right)}} \\{= {90\quad {mV}}}\end{matrix}$

To reduce the ripple, the resolution of the digital process should beenhanced (the number of quantizing steps should be reduced). However, toenhance the resolution, expensive parts are required. The power supplyapparatus according to the present embodiment has been developed tosolve this problem and suppress the ripple of the output voltage byaveraging the digital error without enhancing the resolution in adigital process.

According to the power supply apparatus of the present embodiment, thedifference (digital error) between the on-time of a pulse signalcomputed at a certain timing and the on-time actually generated based onthe computed on-time is stored. When the on-time is computed at the nexttiming, the on-time is corrected such that the stored difference iszero. Hereinafter, the difference is referred to as a barometer.

FIG. 21 shows an example. In this example, the resolution of the digitalprocess of the PWM unit 11 is 100 ns. When the computed on-time isrepresented in the order of 100 ns, a rounding up operation isperformed.

When the on-time is computed by the digital filter operation at time T1,a correction value is obtained by adding a barometer value obtained attime T0 to the computed on-time. In this example, 3.35+(−0.07)=3.28 isobtained. A rounding-up operation is performed on the correction value,and 3.3 is obtained as an on-time to be output to the PWM unit 11. Then,the barometer value at time T1 is computed. The barometer value isobtained as the difference between the correction value of the on-timeand the actually output on-time. In the present embodiment,3.3−3.28=−0.02.

The above described process is hereinafter repeated. Thus, the barometervalue is used as data for use in correcting the result in the nextoperation. Therefore, a digital error can be averaged. The on-timecomputing cycle is shorter than the response time (for example, acut-off frequency) of the LC filter of the power supply circuit.

In FIG. 21, a rounding up operation is performed when the computedon-time is in the order of 100 ns. It is obvious that a rounding downoperation or a rounding off operation can be performed. FIGS. 22 and 23show examples of cases where a rounding down operation and a roundingoff operation, respectively, are performed.

FIG. 24 is a flowchart of the process of averaging a digital error. Inthis process, a rounding up operation is performed in the order of theresolution in the digital process on the on-time computed in the digitaloperation. This process is performed at predetermined intervals througha timer interruption, etc. The timer interruption cycle is shorter thanthe response time of the LC filter of the power supply circuit.

Steps S61 through S64 are the same as steps S1 through S9 shown in theflowchart in FIG. 7. The on-time of the pulse signal is computed usingthe digital filter 52 based on the output voltage Vout of the powersupply circuit. In step S65, the on-time computed in step S64 iscorrected using the barometer value stored in the preceding process. Instep S66, a rounding up operation is performed in the order ofresolution in the digital process on the correction value obtained inthe process in step S65.

In step S67, the result of the operation in step S66 is defined as theset on-time, and written to the on-time register 62 of the PWM unit 11.In step S68, the difference between the correction value obtained instep S65 and the set on-time written to the on-time register 62 in stepS67 is stored as a barometer value for the next process.

FIGS. 25 and 26 are flowcharts of the processes of averaging a digitalerror when a rounding down operation and a rounding off operationrespectively are performed on the computed on-time. The processesaccording to the flowcharts are basically the same as the processesdescribed by referring to FIG. 24. Therefore, the explanation is omittedhere.

It has been experimentally confirmed that a ripple of an output voltagecan be reduced by implementing the above described averaging process.The ripple of the output voltage has been lowered to 7 mV under thecondition given in the above example (pulse signal cycle: 20 μs; inputvoltage: 18V; digital resolution: 100 ns).

The embodiment shown in FIGS. 21 through 26 is described assuming thatthe cycle of the pulse signal provided for the switching element 13 isfixed. However, the digital error can be further reduced by setting thecycle variable.

According to the present embodiment, the duty of a pulse to be generatedis determined based on the output voltage of a power supply circuit.Then, an on-time is computed from the predetermined basic cycle and theabove described duty. The computed on-time is rounded off in the orderof the resolution of the digital process of the PWM unit 11 as in theabove example. The on-time obtained in the rounding off contains anerror.

According to the present embodiment, the cycle of a pulse signal iscorrected such that the computed duty may not be changed when thedigital process results in the computed value having an error. Apractical example is shown below. In this example, it is assumed thatthe reference cycle of a pulse signal is 20 μ. Assuming that the dutyD=15.75% is obtained by the digital filter operation, the on-time iscomputed from the above described reference cycle and the duty D.

20 μs×0.1575=3.15 μs

Assuming that the resolution of the PWM unit 11 is 100 ns, 3.2 μs isobtained as the on-time to be written to the on-time register 62 by therounding off operation. Then, the pulse cycle is corrected such that theon-time to be output and the pulse cycle can maintain the duty obtainedby the digital filter operation. That is, the pulse cycle is correctedby the following equation. cycle Ts=on-time to be written to on-timeregister 62/duty D=3.2 μs÷0.1575=20.3174 μs

The pulse cycle obtained by the above described operation is rounded offin the order of the resolution of the digital process of the PWM unit11. As a result, 20.3 μs is obtained as a pulse cycle to be written tothe cycle register 61.

According to the method of the present embodiment, the on-time to bewritten to the on-time register 62 contains a digital error, but theratio of the pulse cycle to be written to the cycle register 61 to theon-time to be written to the on-time register 62 is a value close to theduty computed according to the output voltage of the power supplycircuit. Therefore, the ripple of the output of the power supply circuitcan be minimized.

FIG. 27 is a flowchart of the process of reducing the digital errorwhile changing a pulse cycle. In this example, the reference cycle of apulse signal is predetermined.

Steps S71 through S73 are the same as steps S1 through S5 in theflowchart in FIG. 7. In step S74, an on-time is computed based on thepredetermined pulse cycle and the duty computed in step S73. In stepS75, a rounding off operation is performed on the on-time obtained instep S74 in the order of the resolution of the digital process. Theoperation result is defined as a set on-time.

In step S76, the set cycle is obtained based on the set on-time obtainedin step S75 and the duty computed in step S73. Then, in step S77, theset on-time obtained in step S75, and the set cycle obtained in step S76are written to the on-time register 62 and the cycle register 61,respectively.

In the above described step S75, the rounding off operation isperformed, but the rounding up or the rounding down operations can alsobe performed.

The maximum value of the ripple of the output voltage generated by themethod shown in FIG. 27 is estimated as follows. It is assumed that theconditions are the same as those in the above described example(reference cycle of pulse signal: 20 μs, input voltage: 18 volt, anddigital resolution: 100 ns).

When a value in the order of 10 μs is 5 in the rounding off operation,an error indicates the maximum value. Therefore, it is assumed that thecomputed on-time is 3.05 μs. In this case, 3.1 μs is written to theon-time register 62. In addition, since the duty of the pulse signal is3.05/20, the correction value of the pulse cycle is obtained by thefollowing equation. $\begin{matrix}{{Ts} = \quad {20\quad {µs} \times \left( {3.1\quad {{µs}/3.05}\quad {µs}} \right)}} \\{= \quad {20.327\quad {µs}}} \\\left. \rightarrow\quad {20.3\quad {µs}\quad \left( {{as}\quad {rounded}\quad {off}} \right)} \right.\end{matrix}$

Therefore, the duty of the pulse signal actually generated by the PWMunit 11 is obtained as follows.

D=3.1÷20.3=0.1527

The duty computed in the digital filter operation is output as follows.

D=3.05÷20=0.1525

Therefore, the duty error is 0.13%, and the ripple of the output voltageis obtained as follows. $\begin{matrix}{{Vripple} = {18\quad {volt} \times \left( {0.1525 - 0.1527} \right)}} \\{= {{- 3.6}\quad {mV}}}\end{matrix}$

According to the above described embodiment, the method shown in FIGS.21 through 26 and the method shown in FIG. 27 are described separately.However, these methods can be combined. For example, when the process inthe flowchart shown in FIG. 24 is combined with the process in theflowchart shown in FIG. 27, the on-time to be written to the on-timeregister 62 is first determined, and then the processes in steps S76 andS77 are performed.

Third Embodiment

The third embodiment relates to the technology of reducing the powerconsumption by changing the operation of the power supply apparatus,which itself depends on the current demanded by a load. Morespecifically, it relates to the technology of reducing the powerconsumption by changing the operation of the power supply apparatusitself when a personal computer, etc. is switched from the normaloperation mode to the suspend mode (or sleep mode).

When a personal computer, etc. enters a suspend mode, the consumedcurrent is considerably reduced with no substantial fluctuation in theconsumed current. In this case, the output current of the power supplyapparatus mounted in the personal computer is significantly reduced withno substantial fluctuation in the output current. Under the conditionthat the output current is thus reduced and small in fluctuation, theload (personal computer, etc.) is not seriously affected even if theresponse speed of the power supply apparatus is low.

When the power supply apparatus according to the present embodimentdetects that the load has entered the suspend mode, it reduces thecurrent consumption of the power supply apparatus itself by lowering thegain and lengthening the cycle of sampling the parameter relating to theoutput of the power supply apparatus.

FIG. 28 shows the function of collecting various parameters in the powersupply apparatus according to the present embodiment. Parameters such asthe output voltage Vout, the output current Iout, and the input voltageVin of the power supply circuit, the temperature in the vicinity of thepower supply apparatus, etc. are input to the multiplexing unit 34 asdescribed above by referring to FIG. 2 or 4. The multiplexing unit 34sequentially outputs parameters input according to the sampling signalfrom the processor 41. The sampling cycle is, for example, described inthe program executed by the processor 41, or preliminarily set in theROM 42. The processor 41 outputs a sampling signal for each samplingcycle, and the multiplexing unit 34 transmits the parameter inputaccording to the sampling signal to the A/D conversion unit 35.

The A/D conversion unit 35 converts a parameter input from themultiplexing unit 34 into digital data. The output from the A/Dconversion unit 35 is read by the processor 41 in a polling process. Thepolling cycle is basically equal to the sampling cycle, but can be setindependently of the sampling cycle.

The process of the flowchart shown in FIG. 7 is performed insynchronization with a sampling signal and the polling process. In thiscase, the duty of a new pulse signal is determined each time eachparameter is sampled, and the PWM unit 11 generates a pulse signalaccording to the newly determined duty.

FIG. 29 shows a part of the program executed by the processor. Theprogram executed by the processor 41 contains programs to be executed inthe normal mode and in the suspend mode. Each program contains anequation describing the feature of the digital filter, a sampling cycle,and a polling cycle.

A feature of the digital filter is described by the equation (3) above(containing the equations (4) through (6)). Equations described in anormal mode program and a suspend mode program are different from eachother in factors A through C. Practically, the cut-off frequency definedby the equation described in the suspend mode program is lower than thecut-off frequency defined by the equation described in the normal modeprogram. FIG. 30 shows the gain of the power supply apparatus obtainedby these two programs.

Both sampling cycle and polling cycle depend on the operation mode of aload. That is, the sampling cycle and the polling cycle described in thesuspend mode program are shorter than the sampling cycle and the pollingcycle described in the normal mode program. Practically, for example,each cycle in the normal mode is set to 50 μS, and each cycle in thesuspend mode is set to 500 μs through 5 m.

FIG. 31 is a flowchart of the process of switching the operations of thepower supply apparatus depending on the operation mode of a load. Theprocesses are performed for each sampling cycle, or the processes of theflowchart shown in FIG. 7 are performed in parallel. In this example,the processes are performed while the power supply apparatus isexecuting a normal mode program.

In step S81, the output current Iout of the power supply circuit isobtained. Then, in step S82, it is determined whether or not the outputcurrent Iout obtained in step S81 is weaker than a predeterminedthreshold current Ith. The threshold current Ith is a reference valuefor determining whether or not a load is operating in the normal mode orthe suspend mode.

If the output current Iout is weaker than the threshold current Ith,then it is assumed that the load has entered the suspend mode, and asuspend mode program is activated in step S83. When the suspend modeprogram is activated, the sampling cycle and the polling cycle areshortened, and the gain of the power supply apparatus is reduced. If theoutput current Iout is equal to or stronger than the threshold currentIth, then it is assumed that the load is operating in the normal mode,and step S83 is omitted.

As described above, when the sampling cycle is extended, the frequencyof the execution of the converting process by the A/D conversion unit 35decreases. Therefore, the power consumption at the A/D conversion unit35 is reduced. Furthermore, when the polling cycle is extended, thefrequency of performing the operations by the processor 41 decreases asshown in FIG. 32, and the wait time is prolonged, thereby reducing thepower consumption of the processor 41.

In the example above, the operations of the power supply apparatus areswitched when the output current Iout becomes weaker than the thresholdcurrent Ith. However, the operations of the power supply apparatus canbe switched according to other triggers. For example, some CPUs have afunction to notify the power supply apparatus of the switch of theoperation modes of the power supply apparatus. For such a load, thepower supply apparatus switches the operations according to thenotification of the load.

When it is determined that the load has entered the suspend mode in theabove described example, the operations of the power supply apparatusare immediately switched. However, when it is actually detected that theload has entered the suspend mode, the normal mode program and thesuspend mode program are first executed in parallel. Then, the operationresult of the normal mode program is output to the PWM unit 11 until theoperation result of the normal mode program and the operation result ofthe suspend mode program match each other, or until a predetermined timehas elapsed since the suspend mode program was activated. Then, theoperation result of the suspend mode program is output to the PWM unit11. Then, the execution of the normal mode program is stopped. With theconfiguration above, stable control can be secured even at a timing whenthe operations of the power supply apparatus are switched.

When a polling cycle is set long, a suspend mode program indicates smallpower consumption. Therefore, the suspend mode program shows a slightincrease in power consumption for the entire power supply apparatus evenif it continues functioning regardless of the operation mode of theload. With the configuration, the operations of the power supplyapparatus can be immediately switched.

FIG. 33 shows the sequence of the process of switching the operationsaccording to the notification from the load. In this example, it isassumed that the load (CPU, etc.) is operating in the normal mode, andthe power supply apparatus is executing a normal mode program. In thenormal mode program, a high-speed response digital filter is used. Onthe other hand, in the suspend mode program, a low-speed digital filteris used. Therefore, the each program is described as HF and LF in FIG.33.

When a load transfers its operation mode from the normal mode to thesuspend mode, it first notifies the power supply apparatus of thetransfer. After the notification, the load is immediately switched tothe suspend mode. When the power supply apparatus receives the abovedescribed notification from the load, the power supply apparatusactivates a suspend mode program. Then, the normal mode program and thesuspend mode program are executed in parallel until the operations ofthe suspend mode program become stable. While the programs are executedin parallel, the normal mode program outputs its operation result to thePWM unit 11. When the operation result from the normal mode programmatches the operation result of the suspend mode program, or when apredetermined time has elapsed since the suspend mode program wasactivated, it is assumed that the operations of the suspend mode programbecome stable.

When the operations of a suspend mode program become stable, the powersupply apparatus outputs an operation result to the PWM unit 11 throughthe suspend mode program, and ends the normal mode program.

According to the above described sequence, stable control can be securedeven at a timing when the operations of the power supply apparatus areswitched.

FIG. 34 shows the sequence of the process of switching the operationsaccording to a notification from a load, and shows the case where theload is returned from the suspend mode to the normal mode. Therefore, itis assumed that the power supply apparatus is executing a suspend modeprogram.

When the load transfers its operation mode from the suspend mode to thenormal mode, it first notifies the power supply apparatus of thetransfer. Then, the load waits for mode transfer permission notificationfrom the power supply apparatus.

When the power supply apparatus receives the notification from the load,it activates a normal mode program, and waits for the stable operationof the program. When the operation of the normal mode programstabilizes, the power supply apparatus outputs the operation result ofthe normal mode program to the PWM unit 11, and transmits a modetransfer permission notification to the load. The load receives thenotification, and transfers the operation mode from the suspend mode tothe normal mode.

Thus, when the load transfers from a small current consumption mode to alarge current consumption mode, it actually switches the modes after theoperations of the power supply apparatus are completely switched. Inthis sequence, the malfunction of the load can be prevented.

The conventional power supply apparatus in the PWM system indicates aconstant switching frequency regardless of the operating state.Therefore, even if the output current of the power supply apparatusbecomes weak, the loss in a switching element is equal to the lossindicated when an output current is strong, that is, the efficiency islow. The embodiment described below has been developed to solve theproblem.

According to the present embodiment, the switching frequency is loweredwhen an output current becomes weak. However, it is necessary toheighten the switching frequency so it is much greater than the cut-offfrequency of the LC filter. According to the present embodiment, theswitching frequency is 100 times as high as the cut-off frequency of theLC filter.

Therefore, when the switching frequency is lowered, the cut-offfrequency of the LC filter also has to be lowered. According to thepresent embodiment, an inductor forming part of an LC filter changeswith an electric current. The inductor to be used is, for example, anamorphous core coil. As shown in FIG. 35, a saturable coil L2 can beconnected in series to the amorphous core coil L1.

FIG. 36A shows the current dependency of the inductance of the amorphouscore coil L1 and the saturable coil L2. The amorphous core coil L1 hasthe characteristic that its inductance becomes smaller as an electriccurrent becomes stronger. The saturable coil L2 has the characteristicthat its inductance suddenly increases when an electric current drops.

FIG. 36B shows the cut-off frequency of an LC filter provided with theamorphous core coil L1 and the saturable coil L2. The cut-off frequencyof the LC filter moderately decreases as the output current Iout becomesweaker when only the amorphous core coil L1 is provided as an inductor.When the amorphous core coil L1 and the saturable coil L2 are provided,the output current Iout decreases rapidly in the range in which it issmaller than a predetermined value. While a current consumption of aload is small (for example, the suspend mode of the CPU), the powersupply apparatus has a small influence on the load even if the responsespeed of the control of the output voltage is low as described above.

The power supply apparatus according to the present embodiment changesthe switching frequency with the output voltage Iout in the softwareprocess. Practically, it preliminarily obtains and stores informationabout the relationship between the output current Iout and the cut-offfrequency of the LC filter (refer to FIG. 36B). Then, the power supplyapparatus periodically monitors the output current, extracts the cut-offfrequency corresponding to the monitored current value, and obtains theswitching frequency from the cut-off frequency.

FIG. 37 is a flowchart of the process of changing the switchingfrequency according to the output current. This process is performed atpredetermined intervals by a timer interruption, etc.

In step S91, the output current Iout is obtained. In step S92, thecut-off frequency fc of the LC filter is determined based on the outputcurrent Iout. This process retrieves a cut-off frequency from the memoryin which the graph shown in FIG. 36B is stored. In step S93, theswitching frequency fsw is computed from the cut-off frequency fcobtained in step S92. This process refers to, for example, an operationby multiplying the cut-off frequency fc by 100. In step S94, the pulsecycle is determined from the switching frequency fsw computed in stepS93, and the pulse cycle is written to the cycle register 61 of the PWMunit 11. The pulse cycle is the inverse value of the switching frequencyfsw.

Afterwards, the PWM unit 11 provides a pulse signal of an updated pulsecycle for a generated switching element 13.

FIG. 38 is a flowchart of the process of computing the on-time of thepulse signal according to the updated switching frequency. This processis a variation of the flowchart shown in FIG. 7.

Steps S101 through S103 are the same as steps S1 through S5 shown inFIG. 7. In these steps, the duty of a pulse signal is obtained. In stepS104, the on-time of a pulse signal is computed according to theswitching frequency fsw computed in step S93 and the duty obtained instep S103. It is assumed that the switching frequency fsw computed instep S93 shown in FIG. 37 or the pulse cycle obtained from the switchingfrequency fsw is stored in the operations unit 50. In step S105, theon-time register 62 of the PWM unit 11 is updated using the on-timecomputed in step S104.

In the above described processes, the power supply apparatus lowers theswitching frequency when the output current becomes weaker. Therefore,when the output current is weak, the loss in the switching element 13 issmall. Especially when the saturable coil L2 is used as an LC filter,the cut-off frequency becomes very low if the output current of thepower supply apparatus is smaller than a predetermined value, therebyconsiderably lowering the switching frequency. Thus, a switching losscan be successfully reduced.

The simplest method of realizing the power supply apparatus according tothe above described embodiment is to determine whether the load isoperated in the normal mode or the suspend mode, and to set theswitching frequency to a small value when it is operated in the suspendmode.

The power supply apparatus according to the present embodiment realizesa configuration of a synchronous type. This configuration can berealized by replacing the rectifying diode shown in FIG. 4 with theswitching element 15. Respective diodes are connected in parallel withthe switching elements 13 and 15.

The pulse signals given to the switching elements 13 and 15 are inverseto each other so that the two elements cannot be simultaneously set toan ON state. These two pulse signals are generated by the PWM unit 11.However, since the switching time of the switching elements 13 and 15 islimited, a dead-off time shown in FIG. 39B is defined for the pulsesignals.

However, the switching speed of the switching elements 13 and 15 changeswith the temperature in the vicinity of the power supply apparatus, theinput voltage, the output current, etc. Therefore, the dead-off timecontains a margin.

At the dead-off time, an electric current flows through the parasiticdiodes of the switching elements 13 and 15, and the shot key barrierdiode connected in parallel with the switching elements 13 and 15.However, the on resistance of these diodes is considerably higher thanthat of the switching elements 13 and 15 in the ON state. Therefore, atthe dead-off time, a loss is large.

To solve the above described problem, the power supply apparatusaccording to the present embodiment preliminarily obtains information onthe temperature dependency, the input voltage dependency, and thecurrent dependency of the switching speed of a switching element, storesthe information, and corrects the dead-off time based on the storedinformation such that the dead-off time refers to the smallest possiblevalue.

FIG. 40 is a flowchart of the process of adjusting the dead-off time.The process is performed at predetermined intervals by a timerinterruption, etc.

In steps S111 through S113, the temperature in the vicinity of the powersupply apparatus, the input voltage Vin, and the output current Iout areobtained. In step S114, the dead-off time is obtained based on theparameters obtained in steps S111 through S113. It is assumed that thetemperature dependency, the input voltage dependency, and the currentdependency of the switching speed of the switching elements 13 and 15are already known, and the shortest dead-off time determined based onthe characteristics is stored in memory. In step S115, the dead-off timeobtained in step S114 is written to a dead-off time register 65 of thePWM unit 11 shown in FIG. 41A.

FIG. 42 is a flowchart showing the operation of the PWM unit 11 shown inFIG. 41A. The flowchart shows the process of generating the pulsesignals Q1 and Q2 shown in FIG. 41B. The pulse signal Q1 is provided forthe switching element 13, and the pulse signal Q1 is provided for theswitching element 15.

When the timer 63 is activated (or re-activated) in step S121, the pulsesignal Q1 is switched from an L level to an H level in step S122. Atthis time, the pulse signal Q2 is assumed to indicate the L level. Instep S123, monitoring is performed to determine whether the elapsed timefrom the activation of the timer has reached the on-time Ton. When themonitor time elapses, the pulse signal Q1 is switched from the H levelto the L level in step S124.

In step S125, monitoring is performed to determine whether the elapsedtime from the activation of the timer has reached ‘on-time Ton+dead-offtime Td’. When the monitor time elapses, the pulse signal Q2 is switchedfrom the level L to the H level in step S126. In step S127, monitoringis performed to determine whether the elapsed time from the activationof the timer has reached ‘pulse cycle Ts−dead-off time Td’. When themonitor time elapses, the pulse signal Q2 is switched from the level Hto the L level in step S128. In step S129, monitoring is performed todetermine whether the elapsed time from the activation of the timer hasreached ‘pulse cycle Ts’. When the monitor time elapses, control isreturned to step S121.

By repeating the above described processes, the pulse signal shown inFIG. 41B is generated. The dead-off time is the smallest value dependingon the temperature, input voltage and current. Therefore, the period inwhich an electric current flows through the diode, etc., shown in FIG.39A, can be shortened, thereby reducing a loss.

According to the third embodiment of the present invention, theoperation of the power supply apparatus is changed when the currentconsumption of the load becomes small. There are other configurationswith which the reference value Vref of a digital filter can be madesmall when it is detected that the current consumption of a load hasbecome small.

According to the above described embodiment of the present invention, apower supply circuit is designed to maintain a constant value of anoutput voltage through PWM. However, the present invention is notlimited to this configuration. The present invention can be, forexample, applied to a power supply circuit for controlling the outputvoltage through PFM (pulse frequency modulation).

According to the present invention, the output of a power supply circuitis controlled by software. Therefore, the characteristic andspecification can be flexibly changed. Especially, since the gain andphase of the power supply apparatus are optimized based on variousparameters, the precision of the voltage control can be improved.Furthermore, since the digital error is averaged, the ripple of anoutput voltage is reduced. In addition, since the switching frequency ischanged depending on the operating state of a load, the switching lossindicated when the output current is weak becomes small.

What is claimed is:
 1. A power supply apparatus comprising: a powersupply circuit for generating DC output based on a pulse signal;conversion means for converting a parameter relating to output of saidpower supply circuit into digital data; amplification means foramplifying a difference between the digital data obtained by saidconversion means and a reference value; adjustment means for adjusting acharacteristic of said amplification means based on an input voltage ofsaid power supply circuit; and generation means for generating a pulsesignal to be provided for said power supply circuit based on the outputof said amplification means.
 2. A power supply apparatus comprising: apower supply circuit for generating DC output based on a pulse signal;conversion means for converting a parameter relating to output of saidpower supply circuit into digital data; amplification means foramplifying a difference between the digital data obtained by saidconversion means and a reference value; adjustment means for adjusting acharacteristic of said amplification means based on an output current ofsaid power supply circuit; and generation means for generating a pulsesignal to be provided for said power supply circuit based on the outputof said amplification means.
 3. A power supply apparatus comprising: apower supply circuit for generating DC output based on a pulse signal;conversion means for converting a parameter relating to output of saidpower supply circuit into digital data; amplification means foramplifying a difference between the digital data obtained by saidconversion means and a reference value; adjustment means for adjusting acharacteristic of said amplification means based on a temperature aroundsaid power supply circuit; and generation means for generating a pulsesignal to be provided for said power supply circuit based on the outputof said amplification means.
 4. A power supply apparatus comprising: apower supply circuit for setting a plurality of values for an outputvoltage to be maintained, and generating DC output based on a pulsesignal; conversion means for converting the output voltage of said powersupply circuit into digital data; amplification means for amplifying adifference between the digital data obtained by said conversion meansand a reference value; adjustment means for adjusting a characteristicof said amplification means based on an output voltage of said powersupply circuit; and generation means for generating a pulse signal to beprovided for said power supply circuit based on the output of saidamplification means.
 5. The power supply apparatus according to claim 1,wherein said amplification means is a digital filter.
 6. A power supplyapparatus comprising: a power supply circuit for generating DC outputbased on a pulse signal; conversion means for converting a parameterrelating to output of said power supply circuit into digital data;amplification means for amplifying a difference between the digital dataobtained by said conversion means and a reference value; adjustmentmeans for adjusting a characteristic of said amplification means basedon an input voltage of said power supply circuit, an output current ofsaid power supply circuit, and a temperature around said power supplycircuit; and generation means for generating a pulse signal to beprovided for said power supply circuit based on the output of saidamplification means.
 7. A method of controlling an output voltage of apower supply circuit for generating DC output based on a pulse signal,comprising the steps of: converting a parameter relating to output ofthe power supply circuit into digital data; amplifying a differencebetween the digital data and a reference value using a digital filterthrough which a characteristic is adjusted based on an input voltage ofthe power supply circuit; and generating a pulse signal to be providedfor the power supply circuit based on output of the digital filter.
 8. Amethod of controlling an output voltage of a power supply circuit forgenerating DC output based on a pulse signal, comprising the steps of:converting a parameter relating to output of the power supply circuitinto digital data; amplifying a difference between the digital data anda reference value using a digital filter through which a characteristicis adjusted based on an output current of the power supply circuit; andgenerating a pulse signal to be provided for the power supply circuitbased on output of the digital filter.
 9. A method of controlling anoutput voltage of a power supply circuit for generating DC output basedon a pulse signal, comprising the steps of: converting a parameterrelating to output of the power supply circuit into digital data;amplifying a difference between the digital data and a reference valueusing a digital filter through which a characteristic is adjusted basedon a temperature around the power supply circuit; and generating a pulsesignal to be provided for the power supply circuit based on output ofthe digital filter.
 10. A method of controlling an output voltage of apower supply circuit for setting a plurality of values for an outputvoltage to be maintained and generating DC output based on a pulsesignal, comprising: converting a parameter relating to output of thepower supply circuit into digital data; amplifying a difference betweenthe digital data and a reference value using a digital filter throughwhich a characteristic is adjusted based on an output voltage of thepower supply circuit; and generating a pulse signal to be provided forthe power supply circuit based on output of the digital filter.
 11. Apower supply apparatus comprising: a power supply circuit for generatingDC output based on a pulse signal; detection means for detecting anoperating state of a load connected to the power supply circuit;sampling means for sampling a parameter used for control of the outputof the power supply circuit; conversion means for converting theparameter sampled by said sampling means into digital data;amplification means for amplifying a difference between the digital dataobtained by said conversion means and a reference value; adjustmentmeans for adjusting a characteristic of said amplification meansaccording to a detection result from said detection means; andgeneration means for generating a pulse signal to be provided for thepower supply circuit based on the output of said amplification means.12. A power supply apparatus comprising: a power supply circuit forgenerating DC output based on a pulse signal; detection means fordetecting an operating state of a load connected to the power supplycircuit; sampling means for sampling a parameter used for control of theoutput of the power supply circuit; adjustment means for adjusting asampling cycle performed by said sampling means according to a detectionresult from said detection means; conversion means for converting theparameter sampled by said sampling means into digital data; andgeneration means for generating a pulse signal to be provided for thepower supply circuit based on the digital data obtained from saidconversion means.
 13. The power supply apparatus according to claim 12,wherein: said generation means has a configuration with which digitaldata can be obtained from said conversion means in a polling process;and said adjustment means adjusts a cycle of the polling processaccording to the detection result from said detection means.
 14. A powersupply apparatus having a power supply circuit which has a smoothingcoil and whose DC output is controlled based on a pulse signal;comprising: conversion means for converting a parameter relating to theoutput of the power supply circuit into digital data; adjustment meansfor adjusting a cycle of the pulse signal based on an output current ora coil current of the power supply circuit; and generation means forgenerating a pulse signal to be provided for the power supply circuitbased on the digital data obtained by said conversion means and thepulse cycle adjusted by said adjustment means.
 15. The power supplyapparatus according to claim 14, wherein inductance of said smoothingcoil can be changed according to an electric current.
 16. A power supplyapparatus having a power supply circuit which has a smoothing coil andwhose DC output is controlled based on a pulse signal; comprising:detection means for detecting an operating state of a load connected tothe power supply circuit; adjustment means for adjusting a cycle of thepulse signal based on a detection result from said detection means;conversion means for converting a parameter relating to the output ofthe power supply circuit into digital data; generation means forgenerating a pulse signal to be provided for the power supply circuitbased on the digital data obtained by said conversion means and thepulse cycle adjusted by said adjustment means, wherein inductance ofsaid smoothing coil can be changed according to an electric current. 17.A power supply apparatus having a power supply circuit which has a setof switching elements and whose DC output is controlled based on a pulsesignal provided for the set of switching elements, comprising:conversion means for converting a parameter relating to the output ofthe power supply circuit into digital data; generation means forgenerating a pulse signal to be provided for the set of switchingelements based on the digital data obtained from said conversion means;and adjustment means for adjusting a dead-off time of the pulse signalbased on at least one of an input voltage of the power supply circuit,an output current of the power supply circuit, and a temperature aroundthe power supply circuit.
 18. A method of controlling an output voltageof a power supply circuit for generating DC output based on a pulsesignal, comprising the steps of: detecting a state of a load connectedto the power supply circuit; sampling a parameter for use in controllingthe output of the power supply circuit; adjusting a cycle of thesampling based on the state of the load; converting the sampledparameter into digital data; amplifying a difference between the digitaldata and a reference value using a digital filter; adjusting acharacteristic of the digital filter based on a state of the load; andgenerating a pulse signal to be provided for the power supply circuitbased on the amplified data.
 19. A method of controlling an outputvoltage of a power supply circuit which has a smoothing coil and whoseDC output is controlled based on a pulse signal, comprising the stepsof: converting a parameter relating to output of the power supplycircuit into digital data; determining a cycle of the pulse signal basedon an output current or a coil current of the power supply circuit; andgenerating a pulse signal to be provided for the power supply circuitbased on the digital data and the determined cycle of the pulse signal.